Field of the Invention
The present invention relates to a charger of a secondary battery.
Description of the Related Art
A secondary battery, such as a nickel-hydrogen secondary battery, and a lithium-ion secondary battery, can be charged to be repeatedly used, and is widely used in various electronic apparatuses. As a device for charging the secondary battery, for example, a charger that operates by using a commercial alternating current power source for household use, as a power source, is widely used. Thus, the secondary battery provides great convenience in that it can be easily charged anytime at home or the like by using a charger.
While the secondary battery is charged by the charger, the secondary battery cannot be used. Thus, a user cannot use a desired electronic apparatus. In general, it takes a long time to fully charge the secondary battery from an almost used-up state in many cases. On the other hand, even if the secondary battery is not fully charged (such as being charged by about 50%), it can be often used for a certain amount of time depending on a kind of electronic apparatus. In addition, it is deemed that a user may often desire to immediately use the secondary battery even if the secondary battery during charging is in the middle of reaching full charge.
Unfortunately, the secondary battery generally cannot show a state of charge in its appearance. Conventional chargers generally have a function of displaying completion of charge when the secondary battery is fully charged, but do not include a function of displaying a state of charge of the secondary battery during charging. Thus, there is a problem in that the conventional chargers are difficult to appropriately respond to user's needs of immediately using the secondary battery even if the secondary battery is not fully charged.
As an example of prior art to solve this kind of problem, a charger including a circuit that detects a state of charge of a secondary battery during charging as available capacity, and a display device that displays the detection state, is publicly known (refer to Japanese Patent Laid-Open No. H05-152006, for example). The available capacity of the secondary battery during charging in the prior art is displayed by stepwise display of a plurality of LED indicating lights, or a liquid crystal display unit.
Unfortunately, the prior art described above directly displays only a state of charge of the secondary battery, a user does not clearly know what kind of electronic apparatus is available in the state of charge. That is, the prior art described above makes it difficult for the user to understand what kind of electronic apparatus is available at the time when the secondary battery during charging is in the middle of reaching full charge, and thus there is still a problem in usability.